The present invention relates to a method of voltage controlled oscillator on-line tuning for every speed to a central oscillating frequency of an voltage controlled oscillator (VCO) to be near a value to be locked.
The speed of a Compact Disk Read Only Memory (CD-ROM) device is controlled by a spindle motor. As the data is desired to be read out, the data phase lock loop (data PLL) should extract the channel basic clock out of the EFM signal. In general, a phase lock loop serves to lock the phase of the EFM signal so that the terminal may receive the data read from the pick up head synchronously.
Generally, when the CD-ROM drive estimates the VCODAC according to the frequency of every speed, it is set a proper VCO digital/analog converter (VCODAC) value. Therefore, the VCODAC value at each speed is determined when VCODAC calibration done.
However, the inaccuracy calibration will effect the CD-ROM drive so as not to lock the frequency of a data to be locked due to a too high voltage or a too low voltage of the VCO input, and thus it is failure when reading the data.
Accordingly, the primary object of the present invention is to provide method of VCODAC adjustment of speed, wherein by an analog/digital converter to read the output value of the loop filter, the VCODAC value can be adjusted in time.
A further object of the present invention is to provide a method of VCODAC adjustment of speed, wherein as the pick up head reads the same position, it is unnecessary to be adjusted again. The reading ability of an optical disk drive is improved.
A further object of the present invention is to provide a method of VCODAC adjustment of speed, wherein as the pick up head reads the same position, it is needless to be adjusted again. The reading ability of an optic disk drive is improved.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when reading in conjunction with the appended drawing.